Phosphorus, nitrogen, organic materials, eutrophic salts such as are found in sludge and undecomposed material are deposited in the sediments at the bottom of lakes and bonds, inner bays and rivers, and DO in the sediment is lowered due to increase in oxygen consumption.
In this stage, aqueous eco-systems are disrupted and natural self purification capacity is lost, and the sludge sediments are converted into sulfides. Various kinds of plankton and water blooms are generated using these sulfides as the energy source and the water quality is worsened in an accelerated manner.
Dead bodies of various insects, fishes, algae, aquatic plants, as well as influent soils from fertile areas which are deposited become what is referred to as humus sludge which as the name implies contains a great amount of fermented organic materials containing all sorts of eutrophic salts in high concentration, which are highly effective in promoting growth of vegetation. However, since such deposits elute eutrophic salts such as of phosphorus and nitrogen into water as the result of anaerobic decomposition to cause the plant cycle phenomenon in the natural world and, as a result, remarkably lower the DO, promote putrefactive decomposition and form sulfides under these reductive conditions, which are deposited, for example, at the bottom of lakes and ponds.
Accordingly, the deposits generate malodors such as of methane, butane and hydrogen sulfide, and iron components are converted into iron sulfide to exhibit black brown or dense brown colors. Further, many ingredients change their forms and are dissolved to promote environmental destruction.
Accordingly, transformation of the bottom sludge under reductive conditions is the key to the improvement of water quality and the eco-systems in recovered by the modification for the sediments.
However, the current method of purifying the sediments merely relies on the removal of the sediments by dredging, and more dredging destroys the aqueous eco-systems afterwards appearing as if it were the inside of a roof top water tank with no circulating eco-system.
Once after the eco-systems are destroyed by the removal of sediments by dredging as described above, regeneration of lakes and bonds requires a long time, up to several decades.
For overcoming the foregoing problem, this invention not only is intended to shorten the operation time for the cleaning treatment of sludges and save construction cost but also to recover the resources of the dredged sludge as one positive means for environmental conservation and continuous utilization of resources. Particularly, this invention intends to obtain soils capable of increased production of healthy foods by organic cultivation without using agricultural chemicals which greatly contaminate the environment, destroy natural eco-systems and indiscriminately kill those eco-systems' inhabitant organisms.